This invention relates to a hypodermic syringe assembly and, more particulary, to a unique syringe assembly that may be utilized as a substantially air-free syringe or as a conventional syringe.
Presently, syringes that are constructed to be used with removable, interchangeable needles suffer from the presence of a large dead air space in the distal end of the assembly. This results in the presence of a substantial air bubble when medication is drawn into the syringe, which leads to the inconvenience of purging the air bubble from the syringe before making the injection. Although several different constructions have been proposed and used for making a syringe with a reduced air bubble, it has heretofore been impossible to provide a syringe assembly which has a reduced air bubble as assembled by the manufacturer but which can be disassembled and used as a conventional needle at the option of the user.
One such prior construction which provides an essentially air-free configuration is illustrated and described in U.S. Pat. No. 3,380,450, which issued on Apr. 30, 1968 to W. H. Adelberger. This patent describes a syringe assembly utilizing a needle hub which is positioned within the bore of a projection extending from the syringe barrel. By thus positioning the needle hub, the bore of the projection is substantially filled with the hub and reduces the volume which is normally present with a conventional needle hub arrangement.
Although the needle hub of the Adelberger patent may be removed from the syringe projection by rupturing a seal that is formed during the manufacturing process, the remaining syringe barrel and projection would be rendered useless by this act in that it would thereafter be incapable, as illustrted and described, of accommodating a conventional needle hub and, therefore, the syringe is actually designed to perform only a single function. In addition to the Adelberger device, other attempts have been made to provide syringe assemblies that may be utilized without the necessity of purging the air therefrom prior to use. However, none of the known prior devices have provided such an assembly that can also be utilized, if desired by the user, with a conventional needle hub.